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Transmission studies of Babesia microti in Ixodes ricinus ticks and gerbils.

ABSTRACT: In order to investigate the possible role of Ixodes ricinus as a vector of zoonotic Babesia microti infection in Europe, a European rodent isolate (HK) and a zoonotic American isolate (GI) were studied in transmission experiments. PCR detected B. microti in the blood and spleens of infected gerbils (Meriones unguiculatus) and also in laboratory-induced infections of I. ricinus ticks. B. microti DNA was detected by PCR in all pooled samples of nymphs and the majority of adults that had fed as larvae and nymphs, respectively, on gerbils with acute infection of the European isolate, confirming that I. ricinus could serve as a vector in Europe. The American isolate, GI, proved to be equally infective for larval and nymphal I. ricinus as the HK strain, despite a very different appearance in gerbil erythrocytes. Nymphs infected with the HK and GI strains readily infected gerbils. In contrast to the finding in acute infections, ticks that fed on gerbils with chronic infections of HK and GI did not become infected. It was also found that the HK strain was not transmitted transovarially. The finding that a B. microti strain (GI) from a distant geographical region (United States) can infect and be transmitted by I. ricinus suggests that other European B. microti strains, in addition to the HK strain used here, are probably infective for I. ricinus, supporting the view that infection of humans with European B. microti may be a regular occurrence.

SUBMITTER: Gray J

PROVIDER: S-EPMC140393 | biostudies-literature | 2002 Apr

REPOSITORIES: biostudies-literature

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Transmission studies of Babesia microti in Ixodes ricinus ticks and gerbils.

Gray Jeremy J von Stedingk Lars Victor LV Gürtelschmid Mikael M Granström Marta M

Journal of clinical microbiology 20020401 4

In order to investigate the possible role of Ixodes ricinus as a vector of zoonotic Babesia microti infection in Europe, a European rodent isolate (HK) and a zoonotic American isolate (GI) were studied in transmission experiments. PCR detected B. microti in the blood and spleens of infected gerbils (Meriones unguiculatus) and also in laboratory-induced infections of I. ricinus ticks. B. microti DNA was detected by PCR in all pooled samples of nymphs and the majority of adults that had fed as lar ...[more]

PMID: 11923342

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Project description:BackgroundMigratory birds can cross geographical and environmental barriers and are thereby able to facilitate transmission of tick-borne pathogens both as carriers of infected ticks and as reservoirs of pathogenic microorganisms. Ixodes ricinus is one of the most abundant tick species in the Northern Hemisphere and a main vector of several Babesia species, some which pose a potential threat to human and animal health. At present only two cases of overt babesiosis in humans have so far been reported in Sweden. To better understand the potential role of birds as disseminators of zoonotic Babesia protozoan parasites, we investigated the presence of Babesia species in ticks removed from migratory birds.MethodsTicks were collected from birds captured at Ottenby Bird Observatory, south-eastern Sweden, from March to November 2009. Ticks were molecularly identified to species, and morphologically to developmental stage, and the presence of Babesia protozoan parasites was determined by real-time PCR.ResultsIn total, 4601 migratory birds of 65 species were examined for tick infestation. Ticks removed from these birds have previously been investigated for the presence of Borrelia bacteria and the tick-borne encephalitis virus. In the present study, a total of 1102 ticks were available for molecular analysis of Babesia protozoan parasites. We found that 2.4% of the ticks examined, all I. ricinus, were positive for mammal-associated Babesia species. Out of all Babesia-positive samples, Babesia venatorum was the most prevalent (58%) species, followed by Babesia microti (38%) and Babesia capreoli (4.0%). B. venatorum and B. capreoli were detected in I. ricinus larvae, whereas B. microti was only present in I. ricinus nymphs. This supports the view that the two first-mentioned species are vertically (transovarially) transmitted in the tick population, in contrast to B. microti. The largest number of Babesia-infected ticks was removed from the common redstart (Phoenicurus phoenicurus) and European robin (Erithacus rubecula).ConclusionsThis study reveals that Babesia protozoan parasites are present in ticks infesting migratory birds in south-eastern Sweden, which could potentially lead to the dissemination of these tick-borne microorganisms into new areas, thus posing a threat to humans and other mammals.

Project description:The U.S. lineage, one of the major clades in the Babesia microti group, is known as a causal agent of human babesiosis mostly in the northeastern and upper midwestern United States. This lineage, however, also is distributed throughout the temperate zone of Eurasia with several reported human cases, although convincing evidence of the identity of the specific vector(s) in this area is lacking. Here, the goal was to demonstrate the presence of infectious parasites directly in salivary glands of Ixodes persulcatus, from which U.S. lineage genetic sequences have been detected in Asia, and to molecularly characterize the isolates. Five PCR-positive specimens were individually inoculated into hamsters, resulting in infections in four; consequently, four strains were newly established. Molecular characterization, including 18S rRNA, ?-tubulin, and CCT7 gene sequences, as well as Western blot analysis and indirect fluorescent antibody assay, revealed that all four strains were identical to each other and to the U.S. lineage strains isolated from rodents captured in Japan. The 18S rRNA gene sequence from the isolates was identical to those from I. persulcatus in Russia and China, but the genetic and antigenic profiles of the Japanese parasites differ from those in the United States and Europe. Together with previous epidemiological and transmission studies, we conclude that I. persulcatus is likely the principal vector for the B. microti U.S. lineage in Japan and presumably in northeastern Eurasia. IMPORTANCE:The major cause of human babesiosis, the tick-borne blood parasite Babesia microti, U.S. lineage, is widely distributed in the temperate Northern Hemisphere. However, the specific tick vector(s) remains unidentified in Eurasia, where there are people with antibodies to the B. microti U.S. lineage and cases of human babesiosis. In this study, the first isolation of B. microti U.S. lineage from Ixodes persulcatus ticks, a principal vector for many tick-borne diseases, is described in Japan. Limited antigenic cross-reaction was found between the Japan and United States isolates. Thus, current serological tests based on U.S. isolates may underestimate B. microti occurrence outside the United States. This study and previous studies indicate that I. persulcatus is part of the B. microti U.S. lineage life cycle in Japan and, presumably, northeastern Eurasia. This report will be important for public health, especially since infection may occur through transfusion, and also to researchers in the field of parasitology.

Dataset Information

Transmission studies of Babesia microti in Ixodes ricinus ticks and gerbils.

Publications

Transmission studies of Babesia microti in Ixodes ricinus ticks and gerbils.

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